Foldable mattress



FIG. 1 is a front elevation view of a foldable mattress showing the new design;

FIG. 2 is a back elevation view thereof;

FIG. 3 is a left-side view thereof;

FIG. 4 is a right-side view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof;

FIG. 7 is a perspective view thereof;

FIG. 8 is another perspective view thereof;

FIG. 9 is a perspective view of the foldable mattress in a first folded position;

FIG. 10 is another perspective view thereof; and,

FIG. 11 is a perspective view of the foldable mattress in a second folded position. 

CLAIM The ornamental design for a foldable mattress, as shown and described. 